Applying urea in the molten state to crops

ABSTRACT

Urea is distributed onto the area to be fertilized by dropping particles of molten urea into the atmosphere 20-500 feet over the area such that the molten urea solidifies into small prills before contacting the area to be fertilized.

United States Patent 1 Has'himoto 11] 3,716,350 51 Feb. 13, 1973 [22]Filed:

[ 1 APPLYING UREA IN THE MOLTEN STATE TO CROPS [75] Inventor: SaburoHashimoto, Yorba Linda,

Calif.

[73] Assignee: Union Oil Company, Los Angeles,

Calif.

March 3, 1969 [21] App1.No.: 803,980

[52] US. Cl ..71/28, 71/30, 71/64 DB,

260/555- B, 260/555 C [51] Int. Cl.... ..C05c 9/00, C07c 127/00 [58]Field of Search ..71/29, 28, 30, 64 DB;

[56] References Cited UNITED STATES PATENTS 1,951,513, 3/1934 Meiser etal. ..71/30 X 2,854,482 9/1958 Guyer ..260/555 B Primary Examiner-ReubenFriedman Assistant ExaminerRichard Barnes Att0rneyMilton W. Lee, RichardC. Hartman, Lannas S. Henderson, Dean Sandford, Robert E. Strauss andMichael H. Laird [57] ABSTRACT Urea is distributed onto the area to befertilized by dropping particles of molten urea into the atmosphere20-500 feet over the area such that the molten urea solidifies intosmall prills before contacting the area to be fertilized.

7 Claims, No Drawings APPLYING UREA IN THE MOLTEN STATE TO CROPSDESCRIPTION OF THE INVENTION This invention relates to a novel mode ofapplying urea to crops and forests so as to fertilize the same.

Urea is commonly handled as a solid prill or granule. In conventionalprill forming, a substantially anhydrous urea melt is formed and theurea prills are obtained by dropping the molten urea as discretedroplets through a prilling tower countercurrent to a vertical stream ofair. The solid urea prills are then bagged and transported in bulk bytank car or tank truck to the distributing location where the urea is tobe applied to the soil and/or plants (e.g., citrus trees, forests,pineapple plants, etc.

The present method of shipping, storing and distributing urea as solidgranules or prills is expensive and inefficient. The urea prills are notreadily adaptable to efficient application to the soil. As solids theyrequire laborious handling and distribution and cannot be used with thelabor saving ground and aerial liquid spraying devices.

The object of my invention, therefore, is an improved method of.fertilizing crops, rangelands, and/or forests.

Another object is to facilitate handling and distribution of urea in theapplication of urea and/or ureabased fertilizers to crops and/orforests.

Other and related objects will be apparent from the followingdescription of the invention.

My invention comprises distributing urea in the molten state to cropsand/or forests. In a preferred embodiment, the molten urea is maintainedin contact with ammonia to minimize biuret formation. As will beapparent from the following description, the method of my inventionsubstantially facilitates the handling and distribution of urea.

As stated hereinabove, the invention involves shipping, storing anddistributing urea in the molten state. Urea may be produced in theconventional manner by reacting ammonia and carbon dioxide underpressure to form ammonium carbamate which is decomposed into urea andwater. Ammonia and unconverted ammonium carbamate are flashed from theurea solution. The resulting urea solution is concentrated, preferablymainly by vacuum evaporation to minimize biuret formation, to anessentially anhydrous molten urea (e.g., 97-99 percent urea). Thismolten urea may be pumped directly, without the commonly molten ureadrops into the atmosphere above the area to be fertilized. The moltenurea droplets are crystalpracticed intervening steps of crystallization,melting and prilling, into heated tank trucks and/or tank cars fortransportation to the fertilization site. At the site, the urea melt canbe conveniently pumped from the tank trucks and/or tank cars to a heatedstorage tank from which the melt can be periodically transferred, asneeded, to ground or aerial distribution means. The molten urea may bestored in the elevated ground rig or aircraft in insulated and/or heatedtanks having capacities between about200 gallons and about 7,000 gallonsdepending on the size of the elevated ground rig or aircraft.

The molten urea can be sprayed from the tanks of the ground rig oraircraft through conventional pressure nozzles and/or rotating nozzleslocated, for example, on the wings of the aircraft or, for example,attached to a boom supported by a ground rig and the lized into smallsolid prills by their contact with the air which cools the droplets andsolidifies them into solid particles as they fall upon the crop,rangeland and/or forest. The height or elevation of the dischargenozzles of the ground rig or-the elevation at which the aircraft mustfly'over the'crop is a matter of judgement well known to operatorsskilled in the art and depends upon the particular crop, the area to becovered, relative wind velocity, and size of the prill desired, etc.This height isnormally 20-500 feet, and preferably 50-200 feet. Theheight should be sufficient to permit solidification of the dropletsduring their fall to the ground. Greater heights can be used withoutlimit; however, the height is preferably no greater than 500 feet, mostpreferably no greater than 200 feet to minimize drift. The size of theorifices in the nozzles of the aircraft or ground rig is generallybetween about 0.01 and 2.0 inch and preferably between about 0.5 and 1.5inch. The size and number of nozzles is a matter of mechanical designand varies with the tank capacity, plane size and speed, urea flow rate,prill size desired, etc.

There are several modifications to the above described method which canbe practiced to minimize biuret formation which can occur when the ureais stored for extended time at or above its melting temperature. As isknown in the art, biuret (NH CONI-I- CONH is formed when urea is heatedat or above its 132C. melting point. Solutions of biuret exhibit aphytotoxic effect when applied to plant foliage and for this reasonbiuret generally is an undesirable ingredient of urea when used as afertilizer. To avoid such phytotoxicity, the biuret content of foliarsprays is generally kept below 5 percent, preferably below 1 percent,and is limited to as low as 0.25 percent for citrus tree foliarfertilization. Although biuret is not believed to exhibit comparablephytotoxicity in urea melts applied in the manner of this invention, itis preferred to avoid the formation of biuret in quantities in excess ofthe aforeindicated. The problem of biuret formation can be overcomeherein by (1) shipping crystalline urea as solid, unprilled, needle-likecrystals and melting the crystalline urea prior to use; (2) adding amelting point depressant to the urea to lower its storage temperature inthe molten state; and/or (3) containing the molten urea under ammoniapreferably at superatmospheric pressure to thereby inhibit biuretformation.

Method 3 is preferred since the added processing steps ofcrystallization and" subsequent melting of the urea as well ascumbersome handling of solid urea required in Method 1 are disadvantagesin this method. The expense and urea contamination from a melting pointdepressant in Method 2 is likewise a disadvantage. Therefore a preferredmodification of the invention comprises maintaining the molten ureaunder an ammonia atmosphere at superatmospheric pressure in theshipping, storage and/or ground or aerial distribution tanks. Theammonia can be maintained in the shipping, storage and airplane orground rig distributing tanks at an ammonia pressure of about 50-400p.s.i.g. preferably -250 p.s.i.g. In a preferred modification, the ureain the shipping and storage tanks is maintained under an ammoniapressure over about 100 p.s.i.g., most preferably 200-400 p.s.i.g.,while the urea in the tank of the distributing aircraft or ground rig ismaintained under a lower ammonia pressure, e.g., a pressure of 50-100p.s.i.g. The lower pressures of ammonia, e.g., 50-100 p.s.i.g. canusually be achieved by the autogenic ammonia pressure solely fromammonia formed as a by-product of biuret formation. Preferably, however,ammonia is added, even with low pressure storage, to avoid the biuretformation which accompanies even limited amounts of ammonia formation.In still another embodiment, no ammonia is injected in the distributiontanks with an ammonia pressure of -50 p.s.i.g., preferably 25-50p.s.i.g. maintained by venting excess ammonia" by-product into theatmosphere. In the low pressure modification, the urea is preferablyapplied to the crop in -50 minutes, most preferably 5-20 minutes, whichis prior to the formation of any significant amounts of biuret. Althoughthe high-pressure construction required for maintaining high ammoniapressure does necessitate added expense, the savings in processing,transportation and handling costs by utilization of the method hereinmore than offsets the added expense.

Method 2 may be combined with Method 3 to minimize the need forhigh-pressure containing vessels and application equipment. The urea maybe shipped in a wet" form, e.g., containing 5-30 percent and preferably-20 percent water. The water lowers the crystallization temperature ofthe urea to substantially less than the 132C. melting point of pureurea. To illustrate, urea containing 30 percent water is still liquid atabout 50-60C. Since biuret formation decreases with decreasingtemperature, adding water to a urea melt or, preferably, retaining thewater in the urea product indirectly inhibits biuret formation. It ispreferred, however, to incorporate less than about 30 percent water inthe composition to insure that the urea will solidify when dropped fromthe aircraft or sprayed from the ground rig into the atmosphere and ontothe crop. Other melting point depressants for urea are sodium nitrateand/or potassium nitrate, which, when included in urea at concentrationsof from 1 to 35 weight percent form low-melting eutectics. Since thesedepressants are also plant nutrients they improve the fertilizationactivity of urea. Preferably, the sodium nitrate and/or potassiumnitrate comprise 5-25% of the melt and a particularly useful combinationis -25% sodium nitrate and 3-10 percent potassium nitrate.

The following examples serve to illustrate modes of practicing theinvention.

EXAMPLE 1 Molten anhydrous urea (99 percent purity) is pumped into a20,000 gallon jumbo tank car having a tank rated at 300 p.s.i.g. andequipped with electric coils to maintain the urea at 135C. The tank ispressured to 250 p.s.i.g. by injection of ammonia. The urea istransported to the fertilization site where it is pumped from the tankcar through insulated lines into an insulated 5,000 barrel storage tankrated at 300 p.s.i.g. and having a pressure-relief valve set at 275p.s.i.g. Ammonia at 250 p.s.i.g. is maintained in the tank vapor spaceabove the urea. The molten urea is maintained at about 135C. by electriccoils. A 5,000 gallon portion of the stored molten urea is pumped fromthe storage tank through insulated lines into an insulated, electricallyheated tank on a Martin Mars airplane typical of those used in forestfire fighting. The aircrafts tank rated at about 50 p.s.i.g., isequipped with a relief valve set at 35 p.s.i.g. The tank has a capacityof 5,500 gallons and is located appropriately in the fuselage so thatwhen filled the load is well balanced. After loading about 5,000 gallonsof urea, the Martin Mars airplane ascends to a height of about 100 feetabove a forest area which is to be fertilized. The anhydrous urea meltis pumped from the 5,500 gallon tank through a manifold'system and intotwo 2-inch headers on the underside of each of the wings. Each header isequipped with seven hollow-cone pressure nozzles of 0.140 inch orificediameter. The molten urea is therebybroken up into small liquidparticles as it is forced through the nozzles and forms small solidprills as the droplets fall through the atmosphere and onto the forest.The total residence time of the urea in the Martin Mars tanks is onlyabout 30 minutes such that no significant amount of biuret will form inthe urea.

EXAMPLE 2 A liquid urea composition comprising urea and 15 percent wateris pumped into a 20,000 gallon jumbo tank car rated at 200 p.s.i.g.which is equipped with electric heating coils. The urea is maintained atabout -100C. and ammonia is injected into the tank to reach a pressureof 120 p.s.i.g. The urea is shipped to its destination and is theretransferred to an insulated 20,000 gallon storage tank. The urea ismaintained at 70-100C. and under 200 p.s.i.g. ammonia pressure in thestorage tank. A 5,000 gallon portion is withdrawn from the tank andpumped into the Martin Mars" airplane of Example 1. The airplane ascendsto a height of 200 feet to ensure crystallization of the urea which issprayed into the atmosphere and falls onto the forest in the mannerdescribed in Example 1. The flight is completed in about 40 minutes suchthat no significant biuret will be formed in the urea.

EXAMPLE 3 This example illustrates the beneficial effect of the presenceof ammonia in inhibiting biuret formation. To a bomb was added 100 gramsof molten urea containing 1.10 weight percent biuret. The bomb washeated to and maintained at about 150C. for about 2 hours. The bombpressure was then measured and found to be about 28 p.s.i.g. The bombwas then heated to and maintained at 150C. for 40 hours. The pressurereached p.s.i.g. at the end of this period. The bomb was then cooled andthe urea was removed. The urea was analyzed and found to contain 7.66weight percent biuret.

To a bomb were added grams of molten urea containing 1.10 weight percentbiuret and 14 grams of ammonia. The bomb was closed and heated to andmaintained at C. for 48 hours. The pressure in the bomb was relativelyconstant at 300 p.s.i.g. throughout the run. The bomb was then evacuatedof ammonia, the urea was removed and analyzed to reveal that itcontained only 2.20 weight percent biuret.

Examples l-2 illustrate particular methods of practicing the inventionand the invention should not be limited by the process steps describedin the examples nor by non-essential details described in thespecification but shall be defined only by the following claims andtheir equivalents.

I claim:

1. A method of distributing urea to an area to be fertilized comprisingtransferring urea in the molten state from storage tanks at thefertilization site to a distribution means, maintaining the urea moltenin said means and passing the molten urea from said means into theatmosphere 20-500 feet above the area to be fertilized.

2. The method defined in claim 1 wherein the molten urea is shipped orstored under an ammonia pressure of 50-400 p.s.i.g. prior to beingtransferred to said distribution means.

3. The method defined in claim 2 wherein the urea is urea is maintainedunder an ammonia pressure from- 0-50 p.s.i.g. in said distributionmeans.

7. The method of claim 1 wherein sodium nitrate is added to the moltenurea.

1. A method of distributing urea to an area to be fertilized comprisingtransferring urea in the molten state from storage tanks at thefertilization site to a distribution means, maintaining the urea moltenin said means and passing the molten urea from said means into theatmosphere 20-500 feet above the area to be fertilized.
 2. The methoddefined in claim 1 wherein the molten urea is shipped or stored under anammonia pressure of 50-400 p.s.i.g. prior to being transferred to saiddistribution means.
 3. The method defined in claim 2 wherein the urea isstored and transported under an ammonia pressure of 50-400 p.s.i.g. andis maintained under an ammonia pressure of 50-100 p.s.i.g. whilecontained in said distribution means.
 4. The method defined in claim 1wherein said distribution means is an aircraft.
 5. The method defined inclaim 1 where the urea has a water content of 5-30 percent.
 6. Themethod defined in claim 1 wherein the molten urea is maintained under anammonia pressure from 0-50 p.s.i.g. in said distribution means.